In these days, demand for high performance plastics are more and more increasing and novel polymers with a variety of functions have been developed. Among these plastics, liquid crystalline resins which exhibit optical anisotropy and are characterized in that their molecular chains are aligned in parallel directions in molten state (thermotropic liquid crystalline polymer) have drawn the attention because of their excellent flow and mechanical properties. In addition, depending on the molecular structure, they have high deflection temperatures under load as well as high continuous use temperatures.
The resin compositions made of thermotropic liquid crystalline polymers with such properties filled with fibrous reinforcing agents such as glass fiber or inorganic fillers have been suitably used for a variety of products such as electric and electronic components including computer-related parts, machine components and precision machine components. For example, they have been applied for motor components such as connector, relay case, switch, coil bobbin, condenser, connector, speaker, committator and separator and used for shielding elements such as coil, crystal and IC chip.
On the other hand, the molecules of such thermotropic liquid crystalline polymers as above are easily oriented with even slight shear strength. Accordingly, there are some drawbacks in a molded article, such as the significant difference of the mold shrinkage between in the machine direction (MD) parallel to the material's flow in molding and the transverse direction (TD) to the MD. In other words, the molded article has high anisotropy in mechanical strength. As such, the polymer has poor strength at the weldline when the article has a weldline.
In order to improve such decreased mechanical properties due to the orientation of molecules or the anisotropy at molding, the art has proposed various methods. For example, Japanese Patent Publication (KOKOKU) No. 38007/1993 discloses a method for preparation of aromatic polyesters by polycondensating certain compounds, characterized in that compounds having polyfunctional groups such as 1,3,5-trihydroxy benzene, 3,5-dihydroxybenzoic acid, 5-hydroxy isophthalic acid or functional derivatives thereof are added to the reaction system. With this method, aromatic polyesters with improved molding properties and reduced anisotropy can be obtained without substantially degrading their thermal properties. The publication teaches those multifunctional compounds such as 1,3,5-trihydroxy benzene and the others can provide polymers with good thermal stability because of their less steric hindrance and high reactivity.
However, said method do not provide satisfying effect in improving weld strength and reducing anisotropy in molding shrinkage factors in the thermotropic liquid crystalline polymers.